The invention relates to a hydrophobically modified anionic cellulose ether, such as hydrophobically modified carboxymethyl cellulose.
Processes for preparing polysaccharides, such as cellulose, starch, and guar, having hydrophobic substituents are known in the art. For instance, EP-A-0384167 describes a slurry process, using a diluent system, for preparing water-soluble polysaccharides, in particular hydroxyethyl cellulose (HEC) derivatives, containing alkylaryl substituents having at least about 10 carbon atoms, for use in latex compositions.
The process comprises reacting an ether-substituted polysaccharide with an alkylaryl hydrophobe-containing compound. It is mentioned that as a result of reacting a polysaccharide ether with an alkylaryl hydrophobe, the ether substitution on the polysaccharide provides an increase in hydrophobic substitution as compared with the unsubstituted saccharide. Examples 35 and 36 of EP-A-0384167 show that when using nonylphenyl glycidyl ether a higher alkylarylation efficiency is observed with polysaccharides having a higher ethylene oxide (as hydroxyethyl) molar substitution (MS) value. MS is defined as the average moles of a substituent per mole of sugar repeating unit. With an ethylene oxide MS of 3.5 a hydrophobe MS of 0.059 with an efficiency of 24% was obtained, while with an ethylene oxide MS of 2.3 a hydrophobe MS of 0.025 with an efficiency of 10% was observed. The obtained hydrophobic substitution efficiency therefore is low.
Thus, a disadvantage of this process is that the hydrophobic substitution proceeds with a low efficiency, resulting in a waste of chemicals and a burden on the environment. A further drawback is that the efficiency with which hydrophobic groups are incorporated is dependent on the presence of hydroxyethyl groups per se and only increases with an increasing number of such groups. This is due to the fact that the hydroxyalkyl substituents are more prone to alkylation than the hydroxyl groups on the sugar repeating unit.
Processes for preparing hydrophobically derivatized polysaccharides are also known from EP-A-0566911 and EP-A-0307915. The process of EP-A-0566911 comprises reacting a polysaccharide with an alkyl halide, an alkylene oxide, or a chloroacetic acid in the presence of an alkali, reacting the modified polysaccharide with a hydrophobic alkyl or alkylaryl reagent having 8 to 24 carbon atoms and containing a nucleophilic reactive group selected from a glycidyl ether and an isocyanate, to produce a watersoluble, hydrophobically modified polysaccharide. This hydrophobically modified polysaccharide is subsequently depolymerized by reaction with hydrogen peroxide to the desired level. The following polysaccharides have been hydrophobically modified: poly(vinyl alcohol), carboxymethyl hydroxypropyl starch, methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, hydroxypropyl guar, carboxymethyl hydroxyethyl cellulose, and HEC.
EP-A-0566911 describes, int. al., a slurry process in which use was made of stearyl isocyanate and nonylphenyl glycidyl ether. HEC was modified using hexadecyl glycidyl ether, and the weight percentage of hydrophobe in the (depolymerized) product was from 0.4 to 1.4% (Example 1). This corresponds to a low hydrophobe MS of approximately 0.005 and 0.02, respectively. A similarly low hydrophobe MS of approximately 0.01 was calculated for carboxymethyl hydroxyethyl cellulose (CMHEC) derivatized with hexadecyl glycidyl ether (Table 4, No. 13). Hydrophobic substitution efficiencies could not be calculated on the basis of information given in this publication, but these are estimated to be low as well.
EP-A-0307915 describes a process for preparing water-soluble hydrophobic CMHEC modified with an alkyl, xcex1-hydroxyalkyl, or acyl group having 8 to 25 carbon atoms. In the Preparation Example the hexadecyl hydrophobe only represents 0.7 percent by weight of the cellulose. A hydrophobic substitution efficiency of 6.7% was calculated. The slurry process preferably is carried out by first hydroxyethylating the cellulose, then attaching the hydrophobe, and finally carboxymethylating the product. The processes of EP-A-0566911 and EP-A-0307915 have the same disadvantages as mentioned above for EP-A-0384167, i.e., a low hydrophobic substitution efficiency and the incorporation of hydroxyethyl groups. In particular, these publications do not disclose a process for preparing hydrophobically modified anionic cellulose ethers, e.g. hydrophobically modified carboxymethyl cellulose (CMC), not carrying a hydroxyalkyl group.
Several other processes have been described in the art, in particular relating to the preparation of hydrophobically modified non-ionic cellulose ethers, i.e. U.S. Pat. No. 4,228,277, U.S. Pat. No. 4,243,802, EP-A-0390240, U.S. Pat. No. 5,120,838, U.S. Pat. No. 5,124,445, EP-A-0362769, EP-A-0471866, and U.S. Pat. No. 5,504,123.
In U.S. Pat. No. 5,566,760 a process is described for the preparation of hydrophobically modified guar derivatives.
Finally, EP-A-0189935 describes water-soluble, hydrophobically derivatized, quaternary nitrogen-containing polysaccharides, in particular derived from HEC. Only quaternary ammonium cellulose derivatives are disclosed. HEC is hydrophobically modified by alkylation with a quaternary nitrogen-containing compound, such as 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, and an alkylhalide hydrophobe, for example dodecyl bromide. In Run 35, a low hydrophobe MS of 0.016 was obtained. A hydrophobic substitution efficiency of 13% was calculated. However, it is not always desirable to incorporate a quaternary ammonium group into a hydrophobically modified polysaccharide.
The above-mentioned prior art does not disclose hydrophobically modified anionic cellulose ethers, in particular hydrophobically modified CMC, not carrying a hydroxyalkyl group. The present invention provides such ethers and an economical process for preparing them.
The inventive hydrophobically modified anionic cellulose ether is obtainable by a process comprising reacting an alkali metal cellulose not carrying a hydroxyalkyl group with at least three alkylating reagents A, B, and C,
one or more reagents A being a haloacetic acid, alkali metal haloacetate, alkali metal vinyl sulfonate, or vinyl sulfonic acid,
one or more reagents B having the formula
R1xe2x80x94(OCH2CH(R2))nxe2x80x94P
wherein R1 represents a C2-C7 group, R2 is hydrogen or a methyl group, n is 0-2, and P represents a glycidyl ether group, a 3-halo-2-hydroxypropyl ether group, a 1,2-epoxy group, or a halide, and
one or more reagents C having the formula
R3xe2x80x94(OCH2CH(R2))mxe2x80x94P
wherein R3 represents a C8-C30 group, m is 0-10, and R2 and P have the meaning as described above.